The present invention relates to a system for the discharge and/or distribution of a gas, and more particularly (but not exclusively) to a system for the discharge and/or distribution of a gas selected from hot gas, combustible gas and hot combustible gas.
In many instances, particularly in industrial chemical works and petroleum refineries, hot and/or combustible gas are produced in quantities which vary from time to time, and for reasons of economy, it is desirable to employ the sensible heat and/or heat of combustion of such gases to heat process streams and/or to raise steam. However, such usage can cause certain problems, among which are the following:
(a) When the demand for heat is reduced or zero, the source of the hot and/or combustible gases can be throttled giving rise to problems elsewhere in the works or refinery. PA1 (b) When the hot and/or combustible gas is used of reheating in more than one unit, a variation in the heat-demand by one unit can cause a major upset in the functioning of the other unit(s). PA1 (c) When the hot and/or combustible gas is available in amounts in excess of the corresponding heat requirement, one or more units using the gas may malfunction. PA1 (a) a furnace adapted to burn carbon monoxide contained in a carbon monoxide-containing gas to heat a fluid which is passed through heat transfer means in the furnace; PA1 (b) a boiler adapted to burn carbon monoxide contained in a CO-containing gas to generate steam; PA1 (c) a main conduit for conducting a CO-containing gas from a source thereof to a junction; PA1 (d) a first conduit for conducting CO-containing gas from the junction to the said furnace; PA1 (e) a first control valve means in said first conduit between said junction and said furnace to regulate the flow of CO-containing gas to the furnace, said first control valve means having a maximum closed position in which a selected minimum flow (exceeding zero flow) of CO-containing gas can pass therethrough; PA1 (f) temperature-responsive means responsive to the temperature of fluid which is passed through said heat-transfer means to regulate the opening and closing of said first control valve means so that the temperature of said fluid is maintained within a selected range; PA1 (g) a second conduit for conducting CO-containing gas from the junction to the said boiler; PA1 (h) a second control valve means in said second conduit between said junction and said boiler to regulate the flow of CO-containing gas to the boiler, said second control valve means having a maximum closed position in which a selected minimum flow (exceeding zero flow) of CO-containing gas can pass therethrough; PA1 (i) means responsive to pressure in the second conduit upstream of the second control valve means and operative to regulate the opening and closing of the second control valve means; and PA1 (j) a liquid seal or other pressure-relief means connected to the first conduit between the first control valve means and the furnace; and wherein the combined minimum flow area for CO-containing gas through the first and second control valve means in their maximum closed positions is sufficient to enable CO-containing gas to pass through the main conduit at all times without substantial restriction to its flow.
The foregoing and other problems can all be accommodated to some extent by diverting the hot and/or combustible gas, and a number of schemes for diverting gas to deal with unprogrammed and unprogrammable variations in gas availability and demand are already known.
U.S. Pat. No. 2,734,526 describes a system in which a combustible gas is conducted from a source to a coke oven, and when the gas availability is in excess of the gas requirement at the coke oven (e.g. when the oven is inoperative), a diverting valve means operates to divert the gas to a flare stack where it is ignited. The diverting valve means comprises water seal means including two bell housings in a common chamber and having their lower edges normally below the level of water in respective seal housings. The bells are connected to each other by a link or chain, and when the gas flow to the oven is interrupted, the increase in gas pressure is communicated to the space beneath one of the bells which causes both bells to be raised. The raising of the other bell above its water seal provides communication between the source of gas and the flare stack and also activates a gas-ignition device to ignite the gas at the top of the flare stack.
U.S. Pat. No. 3,285,320 describes a system in which a fuel gas of variable hydrocarbon composition is burned in a process furnace to heat a fluid passing therethrough to a selected temperature. The heating value of the fuel gas is calculated from its density and the heating in the process furnace is regulated by monitoring the temperature of the heated fluid leaving the furnace, calculated therefrom the heat requirement of the furnace to sustain the selected temperature of the heated fluid, deriving from the gas density and correlated gas heating value the gas flow requirement for the heat requirement of the furnace, and varying the gas flow rate as necessary in order to provide the heat requirement of the furnace.
U.S. Pat. No. 3,749,546 describes a gas flare system adapted to burn waste combustible gas in widely varying quantities. The system comprises a manifold supplying a plurality of gas flare pipes connected in parallel to the manifold. One pipe is unvalved so that a flow path is always available for even the lowest flow rate of gas to the flare associated with this one pipe. The flow rate in the said one pipe is monitored and, at a predetermined rate, a valve which normally closes a second pipe is opened to permit gas to flow therethrough to a respective flare associated with the second pipe. Similarly, the flow in the second pipe is monitored, and when the gas rate therethrough attains a selected maximum rate, a normally-closed valve in a third pipe is opened thereby providing a path for gas to a third flare. This cascade of flow-responsive valves in the parallel-connected pipes enables gas to be safely burned in flares over a very wide range of gas rates.
U.S. Pat. No. 3,779,689 is similar to U.S. Pat. No. 3,749,546 but incorporates, in addition, a progressive cascade of steam supply to each flare supply pipe which is arranged to supply stream to one flare pipe before and after the monitored gas rate in another flare pipe is sustained at a rate at which the gas will continue to pass into the said one pipe in order to purge the latter and avoid the risk of explosion and to avoid the formation of smoke.
U.S. Pat. No. 3,852,019 describes a gas flare system for coping with widely-varying gas flow rates. The system comprises a manifold to which are connected a plurality of pipes of progressively smaller cross-sectional flow area. The largest such pipe is immersed deepest in a water seal and the smallest such pipe is immersed least deeply in the same water seal, the other pipe(s) being immersed to intermediate depths in accordance with their flow areas. Each pipe, with the exception of the largest, has a flow meter therein which regulates the rate at which steam is supplied to the flare at which the gas passing therethrough is burned. The gas flow out of the water seal is monitored and the steam supply rate to the flare regulated accordingly. Thus, even for the lowest gas flow rates (through the smallest, least-deeply immersed pipe), the steam rate to the flare will be roughly matched to the gas flow rate thereby mitigating or avoiding smoke formation.
U.S. Pat. No. 3,852,023 describes a gas flare system comprising a gas manifold connected to progressively narrower pipes. The pipes each have an open end beneath the surface of a discrete, respective water seal, and the wider pipes are immersed to greater depths than the narrower pipes so that at low gas flow rates, gas will pass from the manifold through the narrower pipes only and as the gas flow rate increases, gas will additionally flow through the wider pipes. The gas passing through each pipe and its water seal is conducted by a respective conduit to a respective region of an incinerator of progressively increasing width, the arrangement being that the low gas flows from the narrowest pipes are conducted to the narrowest part of the incinerator and higher gas flows from wider pipes are conducted to correspondingly wider parts of the incinerator. As a result, the gas is burned in the incinerator at a region appropriate to its flow rate, thereby effecting efficient combustion with low smoke and noise.
U.S. Pat. No. 4,095,934 describes a system for utilizing waste refinery gases. The system comprises a main manifold for receiving waste and vented combustible gases from refinery process units, a secondary manifold for conducting waste gas from the main manifold to a compressor and thence to various gas treating units and to a fuel gas utilization system, and a gas flare pipe for conducting the remaining waste gas to a flare for disposal. A control valve is located in the secondary manifold upstream of the compressor, and a first pressure sensor is disposed between the control valve and the compressor. When the pressure on the suction side of the compressor exceeds a selected level due to an increase in the gas flow rate into the secondary manifold, a signal is generated which closes the control valve to prevent overloading of the compressor and the fuel gas utilization system. A second pressure sensor is arranged to monitor the pressure in the gas flare pipe, and when the pressure falls to a selected low level, a signal is generated to cause the control valve to close. Thus the system enables the flare to be supplied with at least the minimum gas flow rate to maintain continuous gas combustion at the flare, and gas in excess of that flared is passed to the gas utilization system in an amount not exceeding the capacity of the gas utilization system. It will be appreciated that the system can operate so that no upper limit is imposed on the amount of gas passed to the flare and that the gas passed to the gas utilization system can be completely interrupted.
It is an object of the present invention to provide a system for the discharge and/or distribution of hot and/or combustible gas to at least two units which use the gas and to maintain the gas flow rate to said units within specified maximum and minimum limits.